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Kinetics and Mechanism of Polymerization of Expandable Monomers
Published in Rajender K. Sadhir, Russell M. Luck, Expanding Monomers, 2020
A variety of catalysts have been employed by various workers for the cationic polymerization of spiro ortho ester monomers. Some of the typical catalysts used for cationic polymerization are boron trifluoride etherate, trimethylsulfonium hexafluoroantimonate, methyl trifluoromethane sulfonate, trifluoromethane sulfonate, silicon tetrafluoride, phosphorous pentafluoride, sulfonium salts of arsenic, phosphorous, antimony, and triphenyl carbenium tetrafluoroborate. The reactivity of these catalysts in polymerizing the spiro ortho ester varies. Uno et al.24 have used fifteen different catalysts in polymerizing bicyclo ortho ester out of which BF3OEt2 and triphenyl carbenium tetrafluoroborate showed the highest reactivity. In general, boron trifluoride etherate has been used more frequently in initiating polymerization of spiro ortho esters.
Bionanocomposites
Published in Satya Eswari Jujjavarapu, Krishna Mohan Poluri, Green Polymeric Nanocomposites, 2020
Archita Gupta, Padmini Padmanabhan, Sneha Singh
Kaolinite is a nano-silicate layer with a 1:1 ratio of silicon tetrahedral and an aluminum octahedral sheet with a common sharing plane for oxygen atoms, whereas phyllosilicate has the respective ratio of 2:1 (Miranda-Trevino et al. 2003 and Beyer 2002). Pyrophyllite is a layered silicate with a respective ratio of 2:1 and any substitution in these layers leads to the development of a new nanoclay called mica. Neither of these clays is easily miscible in water whereas pristine layered silicate with a similar ratio is miscible in water-soluble polymers such as PVA or PEO due to the presence of sodium and calcium ions in the layers (Mousa et al. 2016 and Aranda et al. 1999). To fabricate a hydrophobic polymer soluble nanoclay, ion substitution to some organophilic groups such as alkylammonium, phosphonium, and sulfonium ion is mostly required. Apart from this, functionalization is essential for increasing bond formation between clay and polymer (Manias et al. 2001 and Mousa et al. 2016).
Polymer Technologies
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2020
During the activation of the initiator consisting of a heterocyclic, arylsubstituted, or with aryl-ring-fused sulfonium salt, a carbon-sulfur bond is broken via a ring-opening reaction leading to the formation of a sulfide and a carbocation (carbenium ion) within the same molecule. The functionality of initiators is utilized in various ways to achieve a specific goal. In particular, thermal decomposition of azo initiators such as azo-bis-isobutyronitrile is the most commonly used source of free radicals in the formation of both DVB- and (meth)acrylate-based MIPs. The photochemical decomposition of this compound allows MIPs to be prepared at a low temperature and with a resulting increase in separation efficiency of the polymers (Alexander et al. 2006). Azo-dialkyl peroxides, azo-diacyl peroxides, azo-perestersazo-hydroperoxides, etc. are other examples of initiators used for radical polymerization (Pabin-Szafko et al. 2005). The first three groups of azo-peroxy compounds can play a role of bifunctional initiators in generation of block copolymers. They can also play a role of traditional initiator in radical polymerization of just one type of monomers. Azo-diacyl peroxides and azo-peresters were tested as initiators in styrene and acrylamide polymerization processes and in preparation of block copolymers from vinyl and acrylic monomers (Czech et al. 2008).
Microwave-assisted safe and efficient synthesis of α-ketothioesters from acetylenic sulfones and DMSO
Published in Journal of Sulfur Chemistry, 2023
Based on our previous work [23,24], and the above control experiments, the reaction mechanism with 1a as an exmple substrate can be proposed as presented in Scheme 4. Initially, dimethyl sulfoxide nucleophilically attacks the acetylenic sulfone 1a, producing a zwitterionic intermediate A, which cyclizes into a four-membered ring intermediate B. It further undergoes a 4e ring opening to generate sulfonium ylide 3 [22]. After the formation of the sulfonium ylide 3, dimethyl sulfide is generated through the decomposition of dimethyl sulfoxide with the aid of the ylide 3 under heating [24]. Dimethyl sulfide dissociates into the methylthiyl and methyl radicals. The methyl radical further reacts with the ylide 3 to form a new radical intermediate C, which abstracts a hydrogen atom from dimethyl sulfide to afford the intermediate 4. It shows a silightly different radical process from our previously reported one [24] because the current reaction is perfomed at lower reaction temperature (120 °C) than previous one (160 °C) and the corresonding dimethyl disulfide and dimethylthiomethane were not observed in the current GC-MS anaylsis.
NaSH-HCl mediated reduction of sulfoxides into sulfides under organic solvent-free reaction conditions
Published in Green Chemistry Letters and Reviews, 2020
In Table 1, entries 10 and 11 indicate that the order of addition of the reagents is important. Therefore, protonation is proposed as the initial step, giving protonated sulfoxide A. Indeed, with several sulfoxides dissolution in 37% aqueous solution of HCl was noted. Addition of hydrogen sulfide to A gives sulfonium and oxonium intermediates B, C and D which finally undergo elimination of water and elemental sulfur yielding final sulfide. Sterically hindered and o-substituted sulfoxides require higher amounts of reagents if compared with p- or m-substituted substrates (1cvs. 1f, 1ivs. 1j, 1kvs. 1m, 1ovs. 1p and 1vvs. 1w). One of the potential reasons for such observation might be formation of the sterically hindered tetra substituted species B, C and D.
An efficient manufacturing method for I-shaped cross-sectional CFRP beam with arbitrary arrangement of carbon fiber using electro-activated resin molding
Published in Mechanics of Advanced Materials and Structures, 2020
Kazuaki Katagiri, Shinya Honda, Sayaka Minami, Daiki Kimu, Shimpei Yamaguchi, Takuya Ehiro, Ozaki Tomoatsu, Hirosuke Sonomura, Sonomi Kawakita, Mamoru Takemura, Yayoi Yoshioka, Katsuhiko Sasaki
The electro-activated deposition solution (INSULEED 3030, Nippon Paint Co., LTD, Osaka, Japan) was selected [33, 34]. It is a sulfonium salt of an epoxy group with propargyl alcohol as solvent, and does not contain harmful chemical substances. The epoxy resin is precipitated by energization because a sulfonium reduction precipitation occurs when current flows through the carbon fiber. Sulfur is interposed between carbon fiber and resin to form what is commonly known as the vulcanizing bond. In conventional electrodeposition, a blocking agent is used to prevent any chemical reaction in the solution between the epoxy resin prepolymer and the curing agent [32]. During the heat curing process, the blocking agent is vaporized and a chemical reaction occurs. The blocking agent becomes a volatile organic compound (VOC) that sometimes causes voids. However, the electro-activated deposition solution used in this study depends on the vulcanizing bond, thereby obviating the need for a blocking agent. Therefore, the precipitated epoxy resin during electro-activated deposition does not require refrigerated storage. Also, no metal catalysts were used for the electro-activated deposition reaction.